Most Helpful Guy
Every woman that a man is ever with becomes part of his subconscious harem. (*) While a man may consciously understand and accept a harem member that he was formerly involved with, inside he is a bit torn because you are still his, in a way. Even though you are not officially cheating in any way, subconsciously to him, you did. Depending on the guy, he will respond differently. However, over time (not months but years), when both of you finally have significant history apart, you become a vestigial part of his subconscious harem and things will be fine.
(*) Keep in mind, instinctively, we are polygamous because, from an evolutionary perspective, we diversify and mix up the gene pool more quickly than females and this is the best interests of species survival. However, love has also evolved because that keeps the male around the woman who bore his children and real love overrides his roaming impulse. Now, to varying intensity, a man always has some feelings of love to all harem members. One night stands with just-met women in bars don't get to join the harem, but any woman who was in a romantic relationship with a man joins his subconscious harem. He will always care for her a bit no matter what and, deep down, each man doesn't believe any other man is better at taking care of you (his harem member) than he is. This is one reason why exBFs often help their exGFs or remain friends.
Most Helpful Girl
This happened to me. My ex and I had broken up then he came back to me after he had stuck his dick in some random hoe, let her see him naked, let her see his sex faced, and experience his dick. I was a virgin. It made me feel like he didn't respect me and our relationship otherwise he would have made sure not to harm it even in the slightest. I also didn't want some whore's leftovers.